Electrical measuring apparatus



March 2, 1943. B. c. LANSDALE 4 2,312,s40

ELECTRICAL MEASURING APPARATUS r 7 Filed Jan. 30, 1939' FIG. 5. v

E I INVYEN'T'ORI: 0 db t BEN c, LANSDALE BY W E ATTORNEY Patented Mar. 2, 1943 Benjamin C. Lansdale, San Francisco, Calif., as-

signor to Echlin Manufacturing-Company, San Francisco, Calif., a corporation of California Application January 30, 1939, Serial No; 253,516

' '1 Claims. (Cl. 177-311) This invention relates to improvements in electrical measuring apparatus and, more particularly, to apparatus and methods for measuring or indicating the relative duration of the closure period in an electrical circuit which is intermittently opened and closed.

The present invention may be employed'in any instance where it is desired to determine, in electrical circuits which are intermittently opened and closed at a frequency above a certain minimum, the fractional ratioof the time that the circuit is closed with respect to the time of completed cycle of operation of the circuit, 1. e. the time between two successive closures of the switch. The invention has found application in the internal combustion motor art as a cam angle meter, the purpose and function of which will be now outlined,

In order to secure the most eflicient operation of internal combustion motor ignition, systems, it is necessary: to adjust the breaker contacts of the distributor to remain closed a time in a, predetermined ratio to the time in which the contacts remain separated. The longer the contacts remain closed, the more nearly the time of primary current flow approaches the time required to charge the reactors in the circuit and for the potential to rise to the maximum predetermined by the values of the reactances.

The greater the current flow in the primary at a given motor speed, the higher the induced potential in the secondary and the hotter the spark delivered. However, the current flow should not he high enough to cause undue temperature rise in the coil orexcessive sparking at the breaker points. It is with this attainment of the optimum relative time for contact closure that the present invention is'particularly concerned.

The automotive art has generally adopted the term cam angle to express the relative duration of theclosure period of the contacts, and this term will be adhered to throughout this specification. Cam angle is specifically defined as the number of degrees through. which the distributor cam rotates while the breaker contacts remain closed.

Heretofore it has been the practice to measure the cam angle geometrically by means of a protractor. This operation was carried out tual operation. Slightly loose or worn bushings supportingthe distributor cam shaft, or slight play in the plate upon which the contacts are mounted, may cause, and frequently do cause,

a change in the effective cam angle, when the distributor cam shaft rotates at normal operating speeds from the cam angle which would be measured when the shaft is rotated very slowly.

In an attempt to overcome these disadvantages, several types of cam anglemeters have been developed for measuring the cam angle with the distributor cam shaft rotating at substantially normal speed. Broadly, these meters operate on a common principle. If direct 'current voltage is impressed'across a circuit consisting of a battery, the breaker contacts,;and a voltmeter, all connected in series, and the'contacts successively opened and closed at relatively-high speed, the voltmeter will give a reading proportional to the fraction of time the contacts remain closed with respect to the time of a completed cycle. In other words, the voltmeter will indicate the mean voltage impressed across it, since the rapidity of the intermittent current impulses precludes the voltmeter res'ponding'to' them individually.

These types of 'measuring apparatus required that the breaker contacts be placed 'out of serv-' ice while the measurements were being taken, since the normal high frequency potential oscillations in the ignition circuit would otherwise interfere with the proper functioning of the circuit. One type of'system'provided an auxiliary V make-and-break means to replace temporarily the breaker contacts'in the distributor. This made no provision for timing the spark in proper relation to the 'mechanical operation of the .motor.

This caused erratic operation of the motor while the cam angle was being measured and possible damage to certain parts of the motor. Another system involved running the motor at high speed, opening the'ignition circuit, and then connecting the metering circuit to breaker contacts'to measure the cam'angle while the motor was still turning over under its own momentum. This was disadvantageous since the readings had to be made hurriedly before the motor came to a stop. Furthermore, racing of an internal combustion motor with no imposed lead is damaging to the motor.

The present invention renders it possible to measure the cam angle while the. ignition system is simultaneously functioning in its normal manner. r

Among the objects of the invention'is to filter ,the spirit of the. invention as defined 7 with time.

the high frequency oscillations in the ignition circuit from the metering circuit so as to enable the measuring-- of a substantially direct current potential. 7

Another obiectis-to avoid the use of electronic relays or vacuum tubes which are undesirable 'because 01' their limited life and the inability of the average mechanic to diagnose the cause of trouble in the event of their failure:

Anotherrobject is to provide an apparatus which may be easily calibrated to compensate for difierences in the potential of the batteries.

in the ignition circuits containing. the breaker contacts whose cam angles are to be measured.

Another object is to provide an apparatus which can be readily connected to the ignition Other objects and advantagesappear as this description progresses.

In this specification and the accompanying drawings, the invention is disclosed'in its preferred form. It' is to be understood, however, that it is not limited 'to this form, but may be embodied in other forms without departing from in' the claims following the description.

The present invention is particularly shown and described in connection with its use as a cam angle meter. It, however, will be understood by those skilled in the electrical arts that it may be utilized in other instances where it is desired to determine the duration of the closure period of an electrical circuit relative to the time of the completed cycle of operation where opening and closing of the circuit is recurring at a frequency above a certainminimum. Sucha relative period of closure of an electrical circuit can be measured under the present invention even should it be subject to discontinuous variations, in which case the linear average period of closure at any given moment will be intime, the reading of the meter will similarly vary In'the one sheet of drawings:

Fig. 1 is a schematic wiring diagram of a simple form of measuring apparatus constructed in accordance with this invention and connected to a circuit which is intermittently opened and closed. l

Fig. 2 is a similar diagram of a preferred-form of the invention functioning as a cam angle meter connected tothe conventional ignition system of an internal combustion motor.

. Fig. 3 is a similar diagram of modified iorm of the invention wherein the metering circuit is energized by a source oLsubstantially constant potential.

Fig. 4 is a graph of the potential in a circuit shunted across an impedance in the primary circuit of a conventional ignition system plotted against time and showing the typical transient oscillations occurring when the ignition circuit is opened.

Fig. 5 is a similar graph illustrating the effect of interposing a choke coil in the, shunt circuit. Fig. 6 is a similar graph showing the efiect of an interposed choke coil and one-way impedance in the shunt circuit. r

Fig. '7 is a similar graph of .the potential in the shunt measuring circuit of Fig. 2.

In Fig. 1, the circuit whose period of closure relative to the completed cycle of closing and opening is to be measured, comprises in series a' source of electric potential, such as the battery I, an impedance 2, and theswitch 3 which is opened and closed at'a frequency above a certain minimum. The measuring circuit is shunted across the impedance 2 and includes the meter 4, the variable resistance 5, and the double throw switch 6. Onecontact of the switch 5 is connected back to the battery I through the ground and the ground 1, back to the battery I. The

variable resistance 5 is then adjusted so as to bring the index of the voltmeter 4 over-the graduation marked 100%." The apparatus is now ready for use. p

This preliminary calibration by means of the variable resistance 5 provides a standardized maximum voltage for the meter 4 and thus enables accurate functioning of the apparatus despite diifering' potentials in the circuits to be tested. It is desirable that the actuating means for intermittently opening and closing the switch 3 be in normal operation during the calibration "of the meter 4. The meter4 then will be calibrated against the voltage' of the current source I under normal operating conditions which may be slightly lower than for open circuit conditions due to the current drain through the resistance 2 and the switch 3. g

In making the desired measurement, the switch 6 is thrown. to complete the metering shunt circuit through the contact 8. Current then flows through the meter 4, the resistance 5, the switch 13, the switch 3, and back to the current a source I. If the switch 3 be "opened and closed at a frequency above a certain minimum, say ten cycles per second, the meter 4 will be unable to respond to the individual potential waves impressed thereacross but will give a reading proportional to the average voltage. This average voltage will be in substantially linear proportion to the fraction 01' the time that the switch 3 remains closed with respect to the time'of, its'total'cycl'e of'operation,'thus causing the meter 4 to give a reading indicating this time fraction.

In the embodiment of the invention, above described, the reactan'ces in the circuit are required to berelati'vely low and the meter 4 sufliciently damped to be unaffected by the oscillations attendaht upon the opening of the switch 3. Where the metering apparatus is to'be used inconiunction with circuits having high reactance values therein and consequent marked oscillations associated with the intermittent current flow as in the conventional ignitionsystem of internal combustion motors, the form of the invention shown in Fig. 2 is preferred.

The type of conventional ignition system illustrated in Fig. 2 comprises an input circuit including in series, a current source such as the usual storage battery I 0, with one of its poles grounded at H and its opposite pole connected to the primary l2 of the coil C by the conductor I3. The

input circuit is completed by the conductor l4 connected to the opposite side of the primary l2 and leading through the breaker contacts I! to the ground at l6. These contacts are located in the usual distributor and are intermittently opened and closed by the cam il in synchronism with the operation of the motor. The capacitor l8, in the form of a fixed condenser, is interposed between the conductor I4 and the ground l9 and coacts with the inductivereactor [2 to set up high frequency oscillations in the circuit each time contact at 15 is broken.

The output of the ignition system includes the secondary 20 of the coil C which may be connected to the conductor l3 or otherwise grounded. The usual rotor 2| of the distributor is connected to the opposite terminal of the secondary 20 and completes the circuit through each of the plurality of grounded spark plugs, such as 22, successively. The oscillations in the input circuit set up between the inductive reactor l2 and the capacitor I8, upon the breaking of the contacts i6, induces a high potential in the secondary 20 to generate a spark at 22. This mode of operation is well known to those'skilled in theart and isherein described only to point out the tem is adapted to operate.

The metering shunt circuit shown in Fig. 2 is arranged to block out completely the transient oscillations in the ignition system and to admit to the metering instrument only the intermittent conditions under which the present metering sysuniform fiow of unidirectional current corres spending to the intermittent closing of the contacts i5 and unaffected by thecharacteristic behavior of the reactors I2 and. I8. The shunt .30. One pole of the switch 30 is grounded at 3| while the other pole isconnectable through the conductor 32 to, the terminal of the primary I2 01 the ignition coil C leading 'to the breakerv contacts l5. The-copper oxide rectifier element 33 is connected between the conductors and 29 providing a path parallel to the rectifier element 26, the meter 21, and the resistor 28; The

reversing switch 34 is interposed in the conductors 23 and'29, and enables reversal of the connection of these conductors to the ignition system where the present apparatus is used in conjunction with an ignition system wherein the polarity of the battery 10 is reversed. I The meter 21 may be a voltmeter or a milliainmeter requiring 20 milli amperes for full scale deflection but is graduated either in terms of percent or in degrees. One hundred percent is the maximum reading of the meter in case of its being graduated in percent, or sixty degrees in the case of a meter graduated in degrees andto be used in conjunction with six or twelve cylinder motors. For use in conjunction with four or eight cylinder motors, the meter, if graduated in degrees, would have a maximum reading of ninety or forty-five degrees, respectively. The meter may carry all four scales to permit readings in percent or degrees regardless of the number of cylinders of the motor whose cam angle is being measured.

The choke coil 24 has 300 turns of No. 20 wirelayer wound 91178. form approximately {/2 inch in iable resistor 23 has a maximum resistance of 700 ohms. The copper oxide rectifier elements 28 and 33 eachhave a direct fiow'resistance of 8 to 10 ohms and a reverse flow resistance of 7500 ohms under a potential of 2.0 volts; The values recited are preferred because "they have been found to be most suitable where the present apparatus is to be employed in its principal use in conjunction with the conventional ignition system. It will be obvious, however, to those skilled in the art, that these values may be considerably varied in this and other practical applications 01' the invention.

The rectifier element 26 is arranged to permit the flow of positive'current in the direction of the arrow through the ammeter 21 while imposing a high resistance on thevflow of current in the reverse direction. The rectifier element 33 provides a low resistance bypass path for the fiow. of current in the reverse direction through the shunt circuit thus decreasing the potential of the reverse current across the rectifier element,

26 and thus increasing the effectiveness of the rectifier element 26 in blocking out this current The high resistance of the w irom the meter 21." rectifier 26 to current in the normal direction minimizes the loss of this current throughjthe bypass path. W1

Figs. 4' to '7 diagrammatically .illustrate the effect of the choke coil 24 and the rectifier elements 26 and 33 in filtering out transient oscillations from the metering shunt circuit. Fig, 4 is a graph of the potential E in a substantially non-reactive circuit shunted across the termi nals of the primary 12 of an ignition coil, plotted against the time t showing the typical oscillations occurring when the contacts l5 are broken.

Fig. 5 shows the damping effect of'the choke coil 24 in reducing these oscillations in a shunt circuit wherein'the coil 24 is the sole reactance. It will be noted that, while theoscillations are considerably diminished by the action of the choke coil, they are still marked. Itis unnecessary that the choke coil accomplish more than superficial damping of the oscillations, reducing them to the extent the fluctuation is of negative potential values only, the amplitude of the oscillations being sufficiently damped so that they do not cross the line of zero voltage and thus impress transient positive potentials across the shunt circuit. This requirement being complied with, the unidirectional resistors 26 and 33 will lations from the metering shunt.

vFig. 6 illustrates" theeffect of the choke coil 24 plus the rectifierelement 26. in series, in a shunt circuit across the primary l2; It has been sufiice to block out completely the residual oscilf found that the rectifierelement 26 substantially completely suppresses the damped oscillations passed by the choke coil 24. These oscillations being of negative potential throughout, obviously would be greatly diminished by the high resistance of the opposed rectifier element 26. Their substantially complete diminution is possibly due toa capacitance effect in the rectifier unit. The single wave of negative potential across the shunt circuit arises from the fact that the rectifier element 26 presents only a finite I resistance to current in the reverse direction.

In the shunt circuit of Fig. 2, this single wave of negative potential is completely diverted from .the'meter 21::through; the lowresistance path provided by the. rectifier-element '33. Theinterdiameter and is'of theair core type, andthe var- I mittent'potential impressed across the meter 21 [342, the battery 35,

then assumes auniform positive value as'indicated in Fig. '1.

The procedure in using the apparatus shown in Fig. 2 is substantially the same as for the use of the simplified apparatus of Fig. 1. The conductors 23 and 32 are connected to the terminals of the primary l2 of the ignition coil and the motor started. The switch 30 is thrown to complete a circuit through the ground 3|. Current then fiows from the battery II), the conductors l3 and 23, the choke coil 21, the conductor 25, the rectifier element 26, the meter 21, the resistor 23, the conductor. 29, the switch 30, and back to i the battery through the grounds 3| and II. The potential impressed across the meter 21 is then calibrated against the voltage of the particular battery In by adjusting the potentiometric variable resistance 28 until the index of themeter 21 is brought opposite the dial graduation marked ,l00% or other maximum graduation should the meter be graduated in other units, such as degrees. 1

After the metering apparatusis thus calibrated,

the switch 30 is reversed to complete the shunt circuit-through the conductors 32 and L and the breaker points l5 to the ground l6. '1he voltage impressed across the meter 21 and its consequent reading will then be linearly proportional to the time fraction that the breaker points are closed relative to their complete cycle of operations ashas been herein before described in connection with the simplified embodiment of the invention illustrated in Fig. 1. As the action of tively to the speed of opening and closing of the tical to operate a motor, the pointer will give a V the pointer of the meter is somewhat slow relaconstantreading without substantial oscillations.

, Inthe modified apparatus illustrated in.Fig.' 3, the metering circuit is provided with its own source of current and is arranged so that there is substantially no interchange of potential between the ignition system and the metering subcircuit. This permits the subcircuit to be substantially permanently calibrated with respect to its own source of potential so that the measuring means willgive accurate readings when used in conjunction. with ignition systems having batteries of varyingvoltage, without the necessity for furvoltages in the individual ignition systems. a

In Fig. 3 similar parts of the conventional-ignition system are indicated by reference numerals similar to those in Fig. 2. Parts of the modified metering apparatus corresponding to parts in Fig. 2 are designated by corresponding reference numerals with addition of an a: character.

The modified apparatus comprises, connected in series, the conductor 23.1: adapted to be connected to the battery terminal of the breaker contacts l5, two poles of the reversing switch the choke coil 241:, the rectifier element 261:, the conductor 25'a:, the milliammeter Tim, the adjustable resistor 28m, and the conductor 29:): leading to the ground l6 through til the meter battery 35 can be reversed by means of the reversing switch 343:. The voltage of the battery 35 is such that the potential'it impresseson the conductors 23m and 29:: when the breaker points l5 are separated is somewhat less than the-counterelectromotive force impressed by the battery in. .The battery 35 is consequently unable to produce a reverse current flow the ignition system when the breaker points l5 are opened. Current under the higher potential of the battery I0 is substantially blocked from the metering subcircuit by the high resistance of the opposed rectifier element 26x.v

I'lhe operation of the modified apparatus is analogous to the operation of the form shown in Fig. 2. When the contacts l5 are closed, current flows from the battery 35 through the subcircuit path comprising the conductor 233:, the breaker points I5, th conductor 291:, the milliammeter 21:11, the resistor 281:, the rectifier element 251:, and the choke coil 241:. As before, the meter 21:: will respond to the mean current flowing, and indi"ates the fraction. of the time the points l5 remain closed relative to the time of their completed cycle of operation. The combined action of the choke coil 24:: and the rectifier elements 261: and 33a: filters the high frequency oscillations of the ignition primary from the metering 'subcircuit in the manner hereinbefore discussed in connection with Fig. 2.

Since the maximum deflection of the meter 21a: is dependent only upon the voltage of the battery 35, and not upon the battery H) in an ignition system, the modified apparatus need be calibrated only during its manufacture and at rare intervals to compensate for any deterioration of the battery "35. Closing the switch 30:: connects the conductors 23:1: and 29x, completing a continuous circuit throughthe meter 21m. The potentiometric resistor 28:: is then adjusted un- 211: shows full scale deflection.

While the "useof copper oxide rectifier units at 26 and 33 isgreatly preferred for practical reasons, it is obvious that other types of rectifiers, such as various types of electrolytic cells, electronic relays, etc., could be Substituted Without departing from the spirit of this invention as' rection.

ther calibration to compensate for such varying viclail'risl Current flowing in the direction spending to the normal flow when the breaker points l5 are closed is expressed as flowing in the positive direction, which current in the reverse direction is described as flowing the negative di- Having thus described this invention, what I claim and desire to secure by Letters Patent is:

:1. An apparatus for measuring the time ratio ofthe periods of closure relative to the periods of completed cycles in a main circuit which is intermittently closed and opened at a frequency above a certain minimum to impress a positive potential across an impedance therein, said circuit having inductive and capacitive reactances therein whereby negative potential oscillations of high frequency across said impedance are set up each time said circuit is opened, comprising a metering circuit having its input shunted across said impedance, energy measuring means in said shunt circuit, and rectifying means in said shunt circuit arranged to block the imposition of a 'negative potential on said energy measuring means.

2. Anapparatus for measuring the time ratio of the periods of completed cycles in a maincircuit intermittently closed and opened at a frequency above a certain minimum to impress a potential across an impedance therein, said circuit having inductive and capacitive reactances therein whereby incidental potential oscillations of high frequency across said impedance are set up each time said circuit is opened, comprising a metering circuit having its input shunted across said impedance, energy measuring means in said shunt circuit, a reactance in said shunt circuit having an inductance such that said incidental oscillations will be damped in said shunt circuit, and rectifier means arranged to permit the passage of current through said measuring means only when said main circuit is closed.

3. An apparatus for measuring the time ratio of the periods of closure relative to the periods of completed cycles in a main circuit intermittently closed and opened at a frequency above a certain minimum to impress a. positive potential across an impedance therein, said circuit having inductive and capacitive reactances therein whereby high frequency oscillations of potential across said impedance are set up each time said circuit is opened; comprising a metering circuit having its input shunted across said impedance energy measuring means in said shunt circuit; a choke coil interposed in said shunt circuit adapted to damp said incidental high frequency oscillations therein: a rectifier element in series with said measuring means and arranged to present relatively high resistance to the flow of current in the negative direction therethrough; and a bypass shunted across said measuring means and said rectifier element and adapted to provide a relatively low resistance path to the flow of current in saidnegative direction; and a rectifier element in said bypass adapted to present relatively high resistance to the flow of current in the posi tive direction.

4. A cam angle meter for measuring the period of closure relative to the'completed cycle of the breaker contacts in an internal combustion motor ignition system, comprising a shunt circuit having as its input the primary of the ignition coil in said system, current measuring means in said shunt circuit; a choke coil interposed, in

said shunt circuit adapted to damp incidental high frequency oscillations, a rectifier element of the copper oxide type in series with said measuring means and arranged to present relatively high resistance to the fiow of current in a negative direction; a bypass shunted across said measuring means and adapted to provide a relatively low resistance path to the flow of current in the negative direction, a rectifier unit in said bypass adapted to present a relatively high resistance to the fiow of current in the positive direction, an adjustable resistor adapted to control the potentialimpressed across said measuring' means, and means for connecting said shunt circuit directly to the source of current in said ignition system.

5. Means for measuring the dwellof the periodic breaker means of an ignition system having a source and-an induction coil primary in series with'said means, comprising a voltmeter connected in parallel circuit with saidprimary and a. rectifier in series with the voltmeter in said parallel circuit, the rectifier having such a polarity that said source when applied to'saicl primary is also applied to said voltmeter through minimum resistance, but.when the breaker means disconnects the source the reverse voltage from said primary is applied to said meter through a maximum resistance.

6. Means for measuring the dwell of the periodic breaker means of an ignition circuit having a source of current and an induction coil primary in serie with said breaker means, comprising a current-responsive measuring device connected across an element in said circuit, and a rectifier in series with said measuring device, the rectifier having such a polarity that when current flows through said circuit from said source it is applied to said measuring device through minimum resistance, but when the breaker means disconnects the source of current, the reverse voltage through said circuit is applied to said measuring device through a maximum resistance.

7, Means for measuring the dwell of the peri odic breaker means of an ignition system having a source of current, an induction coil primary, and rbreaker means connected in series,

said means comprising a main circuit connected in parallel with an impedance in said ignition system, said main circuit including a currentresponsive device and an impedance in series,

anda second circuit shunted across said main circuit and including an impedance, the impedance of said second circuit being so arranged that said second circuit ofiers a path of substantially lower impedance to the flow of the current than said main circuit when said breaker means are open.

BENJAMIN C. LANSDALE. 

